Late Quaternary Paleoenvironments and Landscape
Evolution on the Great Bend Sand Prairie

Alan F. Arbogast

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Abstract

Global circulation models (GCM's) project enhanced warming and drying in
the central Great Plains during the next few decades in response to
elevated levels of atmospheric CO2. Given the sensitivity of
sand-mantled landscapes to climate changes, paleoenvironmental research
has focused on the potential response of sand sheets and dune fields to
increased aridity. Although appreciable research has been conducted in
Nebraska, Colorado, and Texas, no detailed information has as yet
emerged from Kansas.

Geomorphic research on the Great Bend Sand Prairie, a large sand sheet
in south-central Kansas, indicates that two late Quaternary
stratigraphic units occur in the region. The oldest deposits are late
Wisconsinan, and the youngest are Holocene. Late Wisconsinan deposits
are widespread, consisting largely of sand and silt (defined herein as
silty sand), and probably accumulated in a very low energy fluvial
environment. Radiocarbon ages from the lower part of the silty sand
range from about 20,000 yr B.P. to around 9,000 yr B.P. At all
localities, the silty sand contains one or two extremely well developed
buried soils with stacked Bt horizons, indicating long-term landscape
stability following deposition. Floral (Picea cf. glauca)
and faunal (e.g.,
Discus cronkhitei) remains, as well as
values
(e.g., -25.6 ) derived from the silty sand indicate that the late
Wisconsinan climate was cooler and had more effective moisture than the
climate during the Holocene. Northwesterly winds prevailed, as
indicated by the orientation of Wilson Ridge, a late Wisconsinan lunette.

Overlying the silty sand are eolian sands of varying thicknesses.
Radiocarbon ages from the upper 5 cm (2 in) of the underlying silty sand
provide an estimate of the maximum-limiting age of dune development. At
three sites, ages on the upper silty sand are late Wisconsinan,
suggesting that overlying eolian sands accumulated during the
Woodfordian. In most instances, however, the upper silty sand dates from
7,000 yr B.P. to 800 yr B.P., indicating that overlying dunes are
largely Holocene deposits.

Mapping of Holocene landforms on uplands recognizes six categories,
ranging from level sand sheets to parabolic dunes. In comparison to late
Wisconsinan deposits, dune sands are well sorted, with a mean particle
size of very fine to fine sand. Values of
(e.g., - 15.0) derived from dunes
imply a warmer climate during the Holocene than the Woodfordian. The
orientation of parabolic dunes indicates prevailing, southwesterly
winds. Dunes usually contain one to two, weakly developed buried soils
with A/AC/C horizonation, representing brief periods of landscape
stability. Calibrated radiocarbon ages at standard deviation
()
on buried soils imply
six periods of pedogenesis during the Holocene, with the center of
probabilities at ca. 6,300, 2,300, 1,500, 1,000, 700, and 200 yr B.P.
Surface soils are generally poorly developed, suggesting that dunes can
easily be mobilized if increased aridity occurs.

Location of major towns, county boundaries, and tributaries on the
Great Bend Sand Prairie.